Methods of objectively evaluating image quality of image data transmitted via a network (which will be referred to as an image hereinbelow) or coded images include methods of using the absolute difference, squared difference, and S/N ratio of pixel values (luminances, color differences, RGB values, etc.) between an original image and an image of interest for evaluation. In the methods, however, a difference between two images is directly reflected on the objective image quality value without taking account of human visual properties, and therefore, there has been a problem that the correlation with a result of subjective evaluation made by a person via visual evaluation is low.
A method relating to the problem is disclosed in Patent Document 1. The image quality evaluation method as disclosed in Patent Document 1 improves the correlation with the subjective evaluation value by applying weighting to the absolute difference, squared difference, S/N ratio or the like as described above based on the power of the alternating-current (AC) components for pixel values while taking account of human visual properties varying with the spatial frequency. It is known that a human visual property is insensitive to signals of higher frequency, and weighting is controlled according to the amount of signals of higher frequency contained in an image.
Patent Document 1: JP-3458600B2